The present invention relates generally to the fabrication of a ring laser, and more particularly to fabrication of a ring laser by epitaxial layer overgrowth (ELOG).
In general, a surface emitting laser can be classified into either a vertical cavity surface emitting laser (VCSEL) or a concentric circular grating surface emitting laser (CCGSEL), wherein the VCSEL includes a semiconductor substrate, such as gallium arsenide, and a VCSEL diode integrated thereon. The VCSEL diode includes a plurality of laterally extending horizontal layers, being arranged one on top of another, in a vertical axial stack including an active cavity region sandwiched between an n-type multiple-layer distributed Bragg reflector (DBR) mirror stack and a p-type multi-layer DBR mirror stack.
The active cavity region contains a plurality of laterally horizontally extending quantum wells. The holes and electrons injected into the quantum wells recombine to emit photons in a process called spontaneous emission. Such photons are emitted in all directions. Numerous reflected trips of such photons back and forth between the DBR mirror stacks ensure to induce stimulated and amplified axial emission, thereby generating an emission of stimulated and amplified axial lasing mode, i.e., VCSEL mode.
In VCSEL's that are fabricated with gallium-nitride(GaN) producing a reflective mirror that is useable for the laser is an issue. The VCSELs are grown on a sapphire substrate that is two to four inches in diameter. The substrate is difficult to scribe and dice causing device yield problems and increasing cost. Another drawback of the VCSEL is its high thermal resistance. Therefore, the high mean thermal density of the VCSEL has restricted applications; e.g., high density array, optical interconnects and signal processing. Since, further, the wavelength λ in the VCSEL mode increases linearly with temperature, the temperature of the active cavity region of the VCSEL must be maintained with negligible variations. Many laser products are in use today in printers, cameras, communication systems and security systems. Many more applications are possible, but the cost of the lasers is typically prohibitive and the supply is limited.